Removed a redundant step which degraded performance

There was a redundant step in blockmap_mesh, that used getTexture( (string) ) altough it had the ID available. This was the major cause of the abusive use of getTextureID( (string) ).
After profiling, it is clearly seen that the overuse of string parsing (mainly using memcmp) was solved.
![texture_improvement](https://f.cloud.github.com/assets/4559873/658381/d7b6d186-d5dc-11e2-9089-2dcc20ceaa32.png)